Add iterkeys and itervalues methods to odict class.

Aldo - 

I made some changes to the ODict class in netlib to add iterkeys() and itervalues() methods so that ODicts behave similarly to Python's native dictionaries.  That said, I didn't change ODict's __iter__ method, so code such as "for i in anODict" returns a header, value list.

I don't know if these methods will of be of any help, but I wanted to assist.

Thanks,
Jason